1. Field of the Invention
This invention relates to a digital video signal recording/reproducing apparatus such as, for example, a digital video tape recorder (VTR) in which a digital video signal is subjected to high-efficiency encoding and recorded in or reproduced from a recording medium.
2. Description of the Prior Art
As a conventional digital video signal recording/reproducing apparatus, the rotary head type digital VTR is available, in which a digital video signal is not subjected to high-efficiency encoding and the pixel data are recorded directly on a recording medium.
Some conventional digital VTRs employ a shuffling process. This shuffling process is a This shuffling process is a process for differing the arrangement of pixels of the video signal from that of pixels to be recorded on a magnetic tape to the largest extent possible. The shuffling process has such effects that errors in the tape head system during reproduction are not concentrated on a reproducing image plane but are instead dispersed to thereby reduce any adverse visual influence, and the reproduced image of a digital VTR in a high speed reproduction mode can be easily visualized. Particularly, in the high speed reproduction mode, the head on a rotary drum obliquely crosses tracks recorded on the tape, so that the signals detected by the reproducing head are skippingly positioned with respect to the recording pattern. With the digital VTR, a high-speed reproducing image plane is formed of only the pixels detected, and if subjected to the shuffling process, the detected pixels are dispersed over the whole area of the image plane, resulting in such an effect that the image plane has no unnatural discontinuity.
On the other hand, a digital VTR using high-efficiency encoding will be considered below. Orthogonal transform encoding is known as an effective encoding method in this case. In orthogonal transform encoding an input video signal is divided into blocks each being composed of, for example, 8 horizontal pixels and 8 vertical pixels, totaling 64 pixels, on the image plane and transformed to the orthogonal components (for example, frequency components) in each block. As the orthogonal transform, the Hadamard transform or discrete cosine transform (hereinafter called DCT) can be used. Of these, the DCT has been commonly used as an orthogonal transform suitable for video information. After orthogonal transformation of each block, the video signal is subjected to variable length encoding and then, compression of the data amount in such a manner that the data of a specific number of blocks are collected to form a segment having a fixed length. In this case, however, when the blocks are shuffled and recorded digitally, blocks of the reproduced image in the high speed reproduction mode are dispersed over the whole area of the image plane. This dispersion is different from the dispersion of pixels, creating such a problem as reduction of image quality. One of the largest factors contributing to degradation in the image quality when reproducing at high speed resides in the luminance signal and chrominance signal, which are different in time from each other forming a block in a high speed reproducing image plane. Accordingly, when reproducing at high speed, different colors are reproduced with respect to the luminance signal not on a pixel by pixel basis but instead, on a block by block basis, each of which is a large area, resulting in a problem in that the color image plane cannot be correctly reproduced.